1. Field of the Invention
This invention relates to a control device for an automatic sewing machine in which a drive mechanism drives a presser unit, according to a sewing pattern stored in memory, which holds a material to be sewed (hereinafter referred to as "a sewing material", when applicable) to form a seam.
2. Description of the Related Art
FIG. 1 is a perspective view showing a conventional automatic sewing machine. In FIG. 1, reference numeral 201 designates a sewing machine table; 202, a needle bar; 203, a thread take-up lever; 24, a drive motor; 25, a mechanism section for converting the rotation of the drive motor 24 into the vertical motion of the needle bar 202 or the swing motion of the thread take-up lever 203; 206, a presser unit for pressing a sewing material to hold it; 207, a shuttle race slide; 208, a bi-axial drive mechanism for moving the pressure unit 206 on the shuttle race slide 207 according to a predetermined pattern; 29 and 30, origin detectors for detecting the mechanical origins of two axes provided for the bi-axial drive mechanism 208; and 209, a control unit for controlling the operations of the above-described components.
The control unit 209 is coupled to an operating panel 40 having a power switch 211, a magnetic data writing and reading means (or a floppy disk driver) 47 (hereinafter referred to as "an FDD 47", when applicable) for writing data in and reading data from a floppy disk 48 (hereinafter referred to as "an FD 48", when applicable) to set sewing patterns and sewing speed. The control unit 209 is further coupled to a foot pedal 31 having a start switch 216 for providing a sewing operation start instruction, and a switch 214 for operating the presser unit 206 (hereinafter referred to as "a presser switch 214", when applicable), and to a stop switch 215 for suspending a sewing operation. Provided on the operating panel 40 are a liquid crystal display unit 217 (hereinafter referred to as "an LCD 217", when applicable) for displaying a procedure of sewing operation, current sewing conditions, error messages, etc., a reset switch 212 for setting the bi-axial drive mechanism 208 at a predetermined position to reset the system, a test switch 213 for driving the two axes without rotation of the spindle of the sewing machine; a speed setting switch 218 for the number of revolutions per minute of the drive motor during sewing; and a group of switches 210 for forming, calling or erasing sewing data as required.
FIG. 2 is a block diagram showing the arrangement of the aforementioned control unit 209. In FIG. 2, reference numeral 1 designates a microcomputer, the center of the control circuit; 32, a crystal vibrator for producing a fundamental frequency for operating the microcomputer 1; 2, an address latch circuit for latching addresses in a memory (a RAM 6 or ROM 7); 3, a memory data buffer for transmitting data from the memory (the RAM 6 or ROM 7) to the microcomputer 1 or vice versa; 4, a periphery data buffer for transmitting data from peripheral elements other than the memory (the RAM 6 or ROM 7) to the microcomputer 1 or vice versa; 5, an IC select signal generating circuit for generating IC select signals for selecting the memory (the RAM 6 or ROM 7) and the peripheral elements, respectively; 6, the aforementioned RAM which is a memory element to which access is made to write or read data; 7, the aforementioned ROM which is a memory element to which access is made only to read data; 8, an I/O for controlling a variety of parallel input signals; 9, a motor drive circuit for operating the drive motor 24; 10, 11 and 12, input interface circuits for receiving control signals and applying them to the I/O 8; and 13, a stepping motor driver which receives through the I/O 8 a feed pulse generated by the microcomputer 1, to control stepping motors 27 and 28 which form the bi-axial drive mechanism 208. Further in FIG. 2, reference numeral 14 designates a solenoid drive circuit for driving a thread cutting solenoid 23; 16, a power supply circuit for supplying electric power to the control circuit; 17, 18, 19, 20, 21 and 22, connectors through which signals lines are connected; 26, a detector for providing synchronous signals (for instance a needle lower position signal) in synchronization with the rotation of the sewing machine and a predetermined number of pulses signals per revolution of the sewing machine (hereinafter referred to as "PG signals", when applicable); 45, a feed pulse delay circuit for determining the timing the microcomputer 1 produces the feed pulse (hereinafter referred to as "a count borrow circuit 45", when applicable); and 44, an interruption controller for causing the microcomputer 1 to generate an interruption signal in response to the output signal of the detector 26 received through the input interface circuit 10.
FIG. 3 is a block diagram showing the count borrow circuit 45 and its peripheral circuits. In FIG. 3, the circuit elements which have been described with reference to FIG. 2 are therefore designated by the same reference numerals or characters. Further in FIG. 3, reference numeral 101 designates a down counter which reads data applied thereto through the I/O 8 by the microcomputer 1, and counts the output PG signals of the detector 26 as many as the value set by the data. The down counter 101 outputs a signal when it is set, or when the contents of the counter is zeroed. Further in FIG. 3, reference numeral 102 designates an OR circuit which provides no output signal when the down counter 101 is set; and 103, a flip-flop circuit for latching (self-holding) the signal of the down counter 101.
FIG. 4 is a part of FIG. 2, a circuit for reading data from the ROM 7 or the floppy disk 48 and writing data in the RAM 6 or the floppy disk 48. In FIG. 4, reference numeral 46 designates a floppy disk controller; and 47, the aforementioned floppy disk driver. The ROM 7 has a system region 7a and a data region 7b . Programs for operating the microcomputer 1 etc. have been stored in the system region 7a . On the other hand, stored in the data region 7b are feed pulse data 220 for the bi-axial drive mechanism 208, start timing data 221 (hereinafter referred to as "count borrow data 221", when applicable), and data 222 for limiting the speed of the sewing machine (hereinafter referred to as "speed limit data 222", when applicable). Those data are provided for the automatic sewing machine only. For instance, count borrow data as shown in FIG. 6 are stored; that is, most suitable count borrow data are stored for stitch lengths in 0.1 mm and numbers of revolutions per minutes, respectively.
The operation of the conventional automatic sewing machine thus organized will be described. The operation of the circuit shown in FIG. 2 has been described in the specifications of Published Unexamined Japanese Patent Application No's 29515/1985 and 54076/1985 in detail. Therefore, mainly the control operation of the bi-axial drive mechanism 208 will be described hereunder.
FIGS. 7, 8 and 9 are flow charts for a description of the control operation of the bi-axial drive mechanism 208 in the conventional automatic sewing machine, and FIG. 26 is a time chart therefor.
In FIG. 26, reference numerals 401, 402, 404, 405, 410 through 416 concern the operations of the conventional automatic sewing machine. More specifically, in FIG. 26, reference numeral 401 designates an needle upper position signal which the detector 26 produces when the needle bar 202 is at the upper position (hereinafter referred to as "an UP signal", when applicable); 402, a needle lower position signal (hereinafter referred to as "a DN signal", when applicable) which the detector 26 produces when the needle bar 202 is at the lower position; 404, the aforementioned PG signal which the detector produces in synchronization with the speed of the sewing machine; 405, a fundamental interruption signal for controlling the stepping motor driver 13 adapted to drive the stepping motors 28 and 27; 410, a borrow signal for controlling the timing of operation of the stepping motors 27 and 28 (hereinafter referred to as "a BR signal 410", when applicable); and 411 and 412, signals representing the drive states of the X-axis and Y-axis stepping motors 27 and 28 (hereinafter referred to as "stepping motor drive signals", when applicable). Further in FIG. 26, reference numerals designate waveforms indicating the loci of movement, in the direction of X-axis and in the direction of Y-axis of the presser unit 206 on the shuttle race slide 207, respectively; 415, a waveform indicating the locus of vertical movement of the thread take-up lever 203; and 416, a waveform indicating the locus of movement of the end of the needle bar 202.
FIG. 7 is a flow chart showing a start inhibit pulse number (or delay pulse number) setting process which is started upon detection of the fall edge 402a of the DN signal 401 output by the detector 26 (hereinafter referred to as "a DN signal interruption process", when applicable). FIG. 8 is a flow chart showing a fundamental interruption signal outputting process which is started in response to the production of the BR signal 410. FIG. 9 is a flow chart showing a stepping motor driving process which is started in response to the production of the fundamental interruption signal 405.
When the start switch 216 is turned on, a sewing operation is started according to sewing pattern data and sewing speed which have been programmed in advance. First the sewing machine mechanism section 25 is driven by the drive motor 24, so that the DN signal 402 is output by the detector 26 as shown in FIG. 26. Upon detection of the fall edge 402a of the DN signal, the DN signal interruption process shown in FIG. 7 is started. First, in Step 501, the microcomputer 1 stores the sewing speed and stitch length of the next stitch in stack. Then, in Step 502, the delay pulse number CBR which corresponds to the sewing speed and the stitch length is stored in stack. Thereafter, in step 503, the microcomputer 1 sets the delay pulse number CBR in the down counter 101 shown in FIG. 3, and applies a reset signal to the flip-flop circuit 103. The process has been accomplished. When the delay pulse number CBR is set in the down counter 101, the BR signal is set to zero level (410a) as shown in FIG. 8. And whenever the detector 26 applies the PG signal 404 to the down counter 101 through the input interface 10, one is reduced from the delay pulse number set therein. When the delay pulse number is reduced to zero, the down counter 101 provides a pulse signal at the BR terminals. as a result of which the output signal, the BR signal 410, of the flip-flop circuit 103 is raised to high level (410b).
When the BR signal 410 is raised to high level, the fundamental interruption signal outputting process is started. That is, in Step 504, outputting the fundamental interruption signal 405 for controlling the stepping motor driver 13 is permitted. Thus, the fundamental interruption signal outputting process has been accomplished.
In response to the fundamental interruption signal 405, the stepping motor driving process is started. That is, whenever the rise edge 405a of the fundamental interruption signal 405 is detected, the stepping motor driving process is effected. First, in Step 505, it is determined whether or not the X-axis stepping motor 27 has moved a distance corresponding to one stitch length. When it is determined that the motor has moved so, Step 507 is effected; and if not, Step 506 is effected. In Step 506, a sub-routine for driving the X-axis stepping motor 27 is executed. For simplification in description, the driving of the stepping motors will not be described. Next, in Step 507, it is determined whether or not the movement of the Y-axis stepping motor 28 has been accomplished. When it is determined that the movement of the motor 28 has been accomplished, Step 509 is effected; and if not, Step 508 is effected; that is, a sub-routine for driving the Y-axis stepping motor is executed. In Step 509, it is determined whether or not the X-axis stepping motor 27 and the Y-axis stepping motor 28 have moved distances corresponding to one stitch length. When it is determined that the motors have moved so, Step 510 is effected; that is, the outputting of the fundamental interruption signal 405 is inhibited, and the stepping motor driving process is ended. When it is determined that the movement of at least one of the motors 27 and 28 has not been accomplished yet, then stepping motor driving process is ended. Thus, the X-axis stepping motor 27 and the Y-axis stepping motor 28 are started substantially at the same time, and when they are moved distances corresponding to a predetermined stitch length, the driving of them is ended.
In the conventional automatic sewing machine thus organized, the presser unit 206 and the thread take-up lever 203 suffer from the following problems in operation which attribute to the above-described control operation. The problems will be described with reference to FIGS. 26, 27 and 28.
By way of example, let us consider the case where a cloth is sewed obliquely according to a sewing pattern as shown in FIG. 27. In FIG. 27, reference character L designates one stitch length; Lx, the horizontal component, or X-component, of the stitch length L; and Ly, the vertical component, ok Y-component, of the same L. In this case, the loci of movement, in the directions of X-axis and Y-axis, of the presser unit 206 on the shutter race slide 107 are as indicated at 413 and 414 in FIG. 26, respectively.
In general, the timing of starting the presser unit 206 is based on various factors. The first of the factors is that, in order that the motion of the needle bar 202 and the movement of the sewing material may not interfere with each other, the movement of the presser unit 206 must be accomplished before the needle of the needle bar 201 pulled out of the sewing material at the time instant G1 is pushed into the latter again at the time instant G2 as shown in FIG. 26. The loci 413 and 414 of movement, in the directions of X-axis and Y-axis, of the presser unit as shown in FIG. 26 satisfy this requirement.
The second factor resides in the relation between the motion of the thread take-up lever 203 and the movement of the presser unit 206. This will be described with reference to FIG. 28. In FIG. 28, the broken line indicates the amount of movement which is obtained by combining the loci 413 and 414 of movement, in the directions of X-axis and Y-axis, of the presser unit 206 in the conventional automatic sewing machine. Further in FIG. 28, reference character B1 designates the bottom dead point of the thread take-up lever 203, and B2, the bottom dead point of the latter 203. While moving between the two points B1 and B2, the thread take-up lever 203 pulls up the thread, and gives tension to it. If, during this period of time, the presser unit 206 is moved, then the upper thread is supplied excessively, as a result of which the tension of the upper thread is decreased as much. That is, in proportion to the movement of the presser unit 206 which takes place while the thread take-up lever moves between the points B1 and B2, the tension of the upper thread is decreased; that is, so-called "sewing condition" is lowered.
FIG. 10 shows periods of time for which the presser unit 206 is movable in the case where two sewing materials a and b different in thickness are sewed. In FIG. 10, reference characters Ha and Hb designate the thicknesses of the sewing materials a and b, respectively; Ga1, Ga2, Gb1 and Gb2, the intersections of the needle connected to the needle bar 202 and the sewing materials; and La and Lb, presser unit movable periods of time. As is seen from FIG. 10, when the thickness of a sewing material changes, it is necessary to change the timing of starting the presser unit 206.
FIG. 11 shows the locus of movement of the presser unit 206 provided in the case where the load weight of the bi-axial drive mechanism is changed for instance by mounting a predetermined jig on the presser unit 206. In FIG. 11, reference character 413a designates a waveform indicating the locus of movement of the presser unit which is under the standard condition; and 413b, the locus of movement of the presser unit provided when the jig is mounted on it. When a load is mounted on the bi-axial drive mechanism 208, the latter 208 is greatly vibrated (sic). If, under this condition, the sewing operation is carried out, then the resultant seam is irregular in stitch. Furthermore, if the speed of rotation of the sewing machine is increased, then the stepping motors 27 and 28 cannot follow instructions output by the stepping motor driver 13; that is, so-called "step out" occurs .
With the above-described first and second factors taken account, it can be readily considered that the ideal and practical timing of starting the presser unit 206 is as indicated at 413 and 414a in FIG. 26. That is, in the case where the stitch length on the side of X-axis is different from that on the side of Y-axis, by delaying the timing of starting the presser unit on the side of the axis where the stitch length is smaller, the movement of the presser unit 206 which takes place while the thread take-up lever 203 moves to the top dead point B2 can be minimized and the tension of the upper thread can be increased. However, in the conventional automatic sewing machine control device, the driving of the bi-axial drive mechanism 208 is started simultaneously as was described above, and therefore it is impossible to obtain the ideal timing of starting the presser unit.
The count borrow data table 221, the feed pulse data table 220, and the speed limit data table 222 have been stored in the ROM 7b, as was described above; however, only one kind of those tables is prepared for one kind of sewing machine. Hence, when the thickness of a sewing material or the load weight of the bi-axial drive mechanism changes, good sewing condition cannot be obtained, or the speed of rotation of the sewing machine cannot be increased.